Morphometric studies in ozone-exposed animals indicate that ozone (O3) toxicity is focal in nature, causing an inflammatory response and epithelial cell injury which are more pronounced in the proximal alveolar region than in other airways. Mathematical simulations indicate that the same airways are the site of maximum O3 dose to tissue. These findings suggest that the internal distribution of O3 dose is an important determinant in the lung response to O3 exposure. Using a newly developed bolus-response method, one can noninvasively measure the fraction of inhaled O3 that is absorbed into intact human lungs in a single breath(f). Moreover, f can be determined as a function of longitudinal penetration from the airway opening (Vp). The long range objectives of this research are: 1. to measure the O3 dose distribution f(V3), in different categories of human subjects under a variety of relevant breathing and pollutant exposure conditions; and 2. use these data as a foundation for building a computer model which gives fundamental insights into the diffusion and chemical reaction processes governing the intake of O3 into lung tissue.